O2 Sensor Replacement, When?
 

Hey guys,

The BMW Service Manual for a 2009 3 series says that their O2 sensors have a warranty of 100,000 miles. They also recommend changing the O2 sensors at 120,000 miles because, according to the manual, O2 sensors wear based on miles driven.

I don't like to replace good, working parts. However, I want to keep my car in good working conditions, and always try to do all the preventative maintenance so that there won't be long term damage to the system. As I understand, the pre cat O2 sensors are responsible for monitoring the air fuel mixture, and can cause not so ideal conditions downstream when they are not at their 100%. My car is currently at 140,000 miles, which to me is a reasonable service life for an O2 sensor. What do you guys think?

If original, you have gotten more than twice the normal miles out of them.

But the sensors have a complete set of diagnostic codes (including a set for tired sensor) and, if there are no problems noted via a code check, why bother.

At the point you get a code, change both matching fronts was my approach. You can safely use Bosch sensors with pigtails. After all, Bosch makes em and Porsche only boxes and stencils a part number on them.

O2 sensors do get lazy with time, if you have nothing better to do with your money, changing them is not a bad idea.

Change them when the car codes and tells you they need to be changed.

I should add...and any muffler shop can replace them if you bring the parts. They have the tools and the longest part of the process is waiting for the system to cool down after the car is driven onto the lift. I had mine done at two different shops and they charged me 1/3 of a labor hour each time they did one.

At 140,000 miles, I'd put money into refurbishing parts of the suspension, steering, and/or cooling systems before replacing the O2 sensors.

I've got code P0430 on and off for a while. I used the Torque app to get some data on the O2 sensors today. If I can trust that my O2 sensors are working properly, do these graphs mean I have two dying CATs?

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